1. Field of the Invention
The present invention relates to a pointer construction with a balance weight which is mounted on a rotor shaft rotating responsively to the rotation of a moving part of an indicating instrument to indicate the value of a measured quantity against scale markings on a dial and, more particularly, to the construction of the pointer having the balance weight molded integral with the pointer and a process of manufacturing the pointer.
2. Description of the Related Art
Generally, used in an indicating instrument for, indicating the value of a quantity measured are electromagnetic instruments using a voltmeter and an ammeter such as a cross coil-type instrument and a moving coil-type instrument, which adopt the rotating pointer construction in which a pointer is fixedly attached nearly at a right angle on the forward end of a connecting rotor shaft through a rotor shaft protruding from the moving part of the instrument or gears, to read the value of the measured quantity by observing the pointer against scale divisions on the dial.
In such an indicating instrument, however, the instrument is usually mounted at a specific angle so that an observer can easily read a value indicated, or the indicator surface is so set at a right angle as to facilitate a normal view to the dial face. The pointer rotating at this mounting angle is affected by the gravity in the position of rotation and indication.
This type of instrument is so constituted as to constantly make indication in a balanced position where a turning torque corresponding to an input quantity and a return spring force are balanced, or in a matching position where a magnet rotates in the direction of compound vector of the magnetic field. Pointer unbalance, therefore, will occur in relation to the center of its rotation. If the pointer is mounted off the center of gravity, the balancing position or the matching position will shift with the effect of the gravity, giving rise to the problem that no accurate rotation and indication of a measured quantity are obtainable.
Therefore, in a conventional indicating instrument, the pointer is fitted with a balance weight in order that the pointer's center of gravity will be positioned at the center of rotation, or that the position of overall center of gravity of the moving part of the instrument and the pointer will be at the center of rotation.
For example, there have been proposed the use of a metal weight which is fixedly mounted in a pointer cap for adjusting the weight unbalance in an extended indicating portion of the pointer as disclosed in the Examined Japanese Utility Model Publication No. HEI 2-49,592, the use of a mass adjusting member such as a screw and a metal plate on the pointer as disclosed in the Japanese Patent Laid-Open No. HEI 2-272,321, and the mixture of a non-magnetic metal powder with a thermoplastic synthetic resin for molding a fine-adjusting balance weight for the balance adjustment of the moving part of the indicating instrument as disclosed in the Examined Japanese Utility Model Laid-Open No. SHO 60-143,366.
According to the conventional process described above, however, it is necessary to install an independent balance weight member separately from the pointer body in the assembly process after completion of the pointer. This process will increase an assembling manhour; furthermore, since the balance weight member is installed and fixed to the pointer by welding, press fitting or other, the pointer mounting position becomes likely to vary, resulting in a failure in accurately balancing the pointer after completion of assembly.
Also in the case of using an adjusting screw or other for mass adjustment after the installation of the balance weight, it is necessitated to perform such a troublesome adjusting operation as increasing or decreasing the mass while observing the indication of the pointer. This operation takes time to complete the pointer.
Furthermore, the pointer balance adjusting weight provided in the moving part of the indicating instrument which is made of a mixture of a synthetic resin and a non-metal powder enables fine adjustment of the weight of the balance weight itself. The mounting of the pointer to the moving part also becomes a troublesome work.